This invention relates to salt flux and more particularly it relates to recovery of salt flux from solutions of rinse liquids used in metallurgical joining operations such as brazing or welding of aluminum members.
In a typical metallurgical joining operation, the aluminum parts to be brazed are joined by an aluminum brazing filler metal, such as an aluminum-silicon alloy, having a melting point slightly below the aluminum members. Brazing is effected by heating the aluminum members to be joined and the filler metal to a temperature above the melting point of the latter, but short of the melting point of the former. The molten filler metal flows and forms a joining fillet between the aluminum metal members. Some diffusion between parent metal and filler metal occurs and the joint is considered, at least to some degree, to be metallurgically bonded.
Normally, an alkali metal halide salt flux is employed to overcome the oxide coating on the parent metal which allows the filler metal to wet and flow over the parent metal surfaces. This is considered necessary to obtain the capillary flow and uninterrupted fillet formation desired. In furnace brazing, the flux is applied as an aqueous flux suspension to the assembled parts which are dried prior to heating to brazing temperature. Typical flux suspensions contain 50% or more of the flux, and they deposit a substantial and easily visible amount of flux on the parts.
In dip brazing, the flux is substantially free of water and the joining operation takes place in the bath. However, in all of these processes, after the joining operation, residual flux salt is washed or rinsed away for purposes of preventing the residual flux salt from corroding the joined members. In the rinsing operation, conventionally, the rinse water is normally discarded when the flux salt dissolved therein reaches a certain level since, thereafter, rinsing is not efficient. Treating the rinse water in this way results in a substantial loss of salt flux which is an economic waste as well as an ecological problem. Thus, it can be seen that there is a great need for a system which is effective in recovering the salt flux from the rinse water. The present invention provides a highly economical system for recoverying salt flux from the rinse water. Furthermore, the present invention eliminates any need to dump or discard the rinse water for reasons of its become ineffective. In addition, the invention can result in as much as an 80% reduction in the loss of salt flux.